1. Field of the Invention
The present general inventive concept relates to generation of ion beams of a semiconductor neutral beam etcher, and more particularly, to an ion beam extractor that controls a direction and an intensity of ion beams by adjusting a voltage applied to a grid having slits formed therein.
2. Description of the Related Art
Recently, according to increasing requirements for integration of semiconductor diodes, a design rule for semiconductor integration circuits has been reduced, requiring a critical dimension of 0.25 um (micrometers) or less. Etchers for ion reinforcement, such as a high-density plasma etcher, a reactive ion etcher, and the like, are typically used to realize this critical dimension of the semiconductor diodes.
In a semiconductor fabrication process, a grid for generation of high ion flux is used to process a wafer with ion beams or neutral beams.
FIGS. 1 and 2 illustrate a neutral beam chamber having a conventional grid 3. As illustrated in FIGS. 1 and 2, the grid 3 used for neutral beam etching has a plurality of circular holes 5 through which ion beams produced by an ion source 1 (plasma) pass to cover an entire surface of a wafer 9. The diameter of each hole is about 3˜6 mm (millimeters).
The grid 3 is located at a rear end of an ion source 1 on a path of the ion beams to accelerate the ion beams using an electric field generated by application of a voltage thereto. At the same time, the grid 3 adjusts energy of the ion beams by focusing the ion beams using the plurality of holes 5 through which the ion beams pass.
A reflector 7 is spaced slightly apart from the rear end of the grid 3 and reflects the ion beams incident thereto and transforms the reflected ion beams into neutral beams. The reflector 7 is slightly slanted with respect to the wafer 9 (at an angle of about 5˜9°) in order to allow efficient etching for a wall of the wafer 9.
When the ion beams generated by the ion source 1 pass through the grid 3, the conventional grid 3 extracts the ion beams passing through the grid 3 and focuses the extracted ion beams to generate the neutral beams, which are used for etching an object film on the wafer 9 of a semiconductor substrate.
An ion flux is influenced by a density of plasma, a shape of the grid 3, a thickness of the grid 3, a size of the grid 3, and the electric field created by applying the voltage to the grid 3. Furthermore, since the grid 3 has the plurality of holes 5, the wafer 9 is typically rotated in order to enhance a uniformity of an etching rate for the wafer 9.
As described above, since the plurality of holes 5 for generating the neutral beams are arranged on an area of the grid 3 corresponding to an area of the wafer 9, and allow the ion beams to pass therethrough, resulting in an ion beam extraction area below 20˜30% of the entire area of a plate on which the wafer 9 is positioned, it becomes necessary to increase the density of the plasma or the electric field.
When increasing the density of the plasma, there is a problem in that a direction of the ion beams is difficult to control by adjusting the electric field due to the fact that the neutral beam chamber typically comprises two or three electrodes in the grid 3.
Additionally, since the wafer 9 is rotated to enhance the uniformity of the etching rate, there is a problem in that an angle of the ion source 1 must be changed in order to change an angle of the ion beams.